You don't need to call plusnet unless you want them to offer you a better deal.
But probably worth doing if you are in contract to confirm that the reason you are leaving is the price hike.
Otherwise Plusnet may charge cancellation fees; which you should get back in the end but with the risk of a lot of hassle.
Make sure you use the migrate
word, not the cancel
word, or they may cancel you entire broadband.
At one time BT were notorious for that for people migrating out; I don't know if Plusnet were but better safe than sorry.
I recently set up the change with Quicdo, but it looks as if Topcashback has had better offers since then.
Moved from BT Infinity 2 to PlusNet. Happy so far, but soon moving back after recent PlusNet changes.